|Focusing screen with a split-image device in|
the centre, surrounded by a microprism ring
In a reflex camera's focusing screen, a Split-Image, sometimes called a split image rangefinder or Split-Prism, is an optical focus-assistance device that displays an image divided in two. When the image is out of focus, the two halves of the image are separated; when in focus, the halves line up to form a single image. The split is often horizontal, but sometimes diagonal.
Split-image devices are often combined with microprisms.